1. Field of the Invention
The present invention relates to a power supply device, more particularly to a power supply device having two resonant converters that are coupled in parallel.
2. Description of the Related Art
Resonant converters are known to have advantages such as high conversion efficiency and low cost, and are hence commonly used in high power isolated DC/DC conversion. Nevertheless, because resonant converters operate on sinusoidal current waveforms, currents generated by resonant converters have high ripple factor even after current rectification. A conventional technique for reducing ripple factor involves phase-shifting output currents of the parallel-connected resonant converters.
However, various factors could affect output currents of the parallel-connected resonant converters, making the output currents non-uniform, and subsequently affecting the conversion efficiency of the resonant converters. Moreover, non-uniformity of the output currents affects the reduction of ripple current.
Therefore, resonant converters operating in a current sharing mode need uniform current control. Referring to FIG. 1, a conventional power supply device 900 includes a first resonant converter 91 and a second resonant converter 92 that are coupled in parallel to provide an output voltage VO. The conventional power supply device 900 has two feedback paths.
The first feedback path involves a voltage controller 93. The voltage controller 93 generates a control signal according to the output voltage VO received from output sides of the first resonant converter 91 and the second resonant converter 92, and provides the control signal to a buck converter 94 so as to control switching frequency of a power switch (not shown) therein, thereby enabling conversion of a 400V signal from a power factor correcting circuit 95 into a 300V input voltage that is provided to the first and second resonant converters 91, 92 by the buck converter 94.
The second feedback path involves a subtractor 96 and a load-balancing controller 97. The subtractor 96 generates a difference signal corresponding to a difference between output currents IOA, IOB received from the output sides of the first and second resonant converters 91, 92. The load-balancing controller 97 generates a driving signal, according to the difference signal generated by the subtractor 96, for controlling switching frequency of a power switch (not shown) of each of the first and second resonant converters 91, 92, thereby controlling the output currents IOA, IOB.
Nonetheless, since the internal circuits of the first and second resonant converters 91, 92 of the conventional power supply device 900 are not identical, control of the switching frequencies of the power switches of the first and second resonant converters 91, 92 to achieve uniform output currents is difficult to implement.